Conventional phase and magnitude detectors typically receive an input voltage and an input current signal and generate a magnitude and phase output signal. The magnitude output signal typically reflects a relationship of the magnitudes of the input signals. The phase output signal typically indicates the phase difference between the input voltage and current signals. In plasma generation systems, phase-magnitude detectors can be implemented in various configurations.
One configuration utilizes un-tuned (broadband) detectors. Examples of the un-tuned detectors include line section samplers used in the matching networks manufactured by the assignee of this subject patent application and sold under the brand name Matchwork®. Un-tuned detectors function well for single-process plasma recipes, and can be configured to function acceptably in the presence of harmonics, where the relative amplitude and phase of the harmonic content remains substantially constant. When process recipes change, harmonics often change, leading to unacceptable performance of the untuned detectors.
Another configuration of a phase-magnitude utilizes tuned phase-magnitude detectors. These detectors address the problem of variable harmonic content by employing bandpass filtering of the sampled voltage and current signals before application to a detector bridge circuit. The detector bridge circuit operates in quadrature phase, allowing diode detectors to discriminate the phase of the incoming signals. Recent dual-frequency systems that produce intermodulation distortion products that are very close (less than 5%) in terms of percent frequency from the desired signal frequency have resulted in phase-magnitude detector performance that is less than optimal.
Another configuration of a phase-magnitude detector utilizes quadrature phase-magnitude detectors. This system uses two quadrature demodulators to perform an analog mix of the two sampled RF voltage and current waveforms to a zero- or low-intermediate frequency (IF). The mixers are driven from a common local oscillator (LO), which is either an amplified reference of the sampled RF signals, or is phase-locked to one or both of the sampled RF signals. The four analog output voltages, the in-phase and quadrature components, from the two quadrature demodulators are then digitally sampled. The digital signals are then processed to provide the magnitude of each original RF sample, and the phase relationship of each, referenced to the LO, and hence each other. This provides the necessary magnitude and phase information of the original sampled RF signals.
One additional configuration of phase-magnitude detectors utilizes exclusive-OR phase detectors. Such detectors include high-speed comparator peak detectors for impedance magnitude.